Diesel exhaust particles enhance lung injury related to bacterial endotoxin through expression of proinflammatory cytokines, chemokines, and intercellular adhesion molecule-1

Epidemiologic studies demonstrate acute and serious adverse effects of particulate air pollution on respiratory health, especially in people who are susceptible to bacterial infection. However, the underlying mechanism remains to be elucidated. To provide experimental evidence for the epidemiologic data, we determined the effects of diesel exhaust particles (DEP), major participants in particulate pollutants, on lung injury related to bacterial endotoxin in mice. Intratracheal instillation of DEPs synergistically enhanced lung injury related to endotoxin from gram-negative bacteria, which was characterized by neutrophil sequestration, interstitial edema, and alveolar hemorrhage. In the presence of endotoxin, DEPs further activated the nuclear translocation of p65 subunit of nuclear factor-kappaB (NF-kappaB) in the lung and increased the lung expression of intercellular adhesion molecule-1, interleukin-1beta, macrophage chemoattractant protein-1, keratinocyte chemoattractant (KC), macrophage inflammatory protein-1alpha, and Toll-like receptors. DEPs given alone increased the lung expression of Toll-like receptor 4 and the nuclear localization of p50 subunit of NF-kappaB. The combined exposure to DEPs and endotoxin decreased nuclear localization of CCAAT/enhancer binding protein beta. These results provide the first experimental evidence that DEPs enhance neutrophilic lung inflammation related to bacterial endotoxin. The enhancement is mediated by the induction of proinflammatory molecules, likely through the expression of Toll-like receptors and the activation of p65-containing dimer(s) of NF-kappaB, such as p65/p50.